首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   20915篇
  免费   2595篇
  国内免费   508篇
耳鼻咽喉   55篇
儿科学   373篇
妇产科学   139篇
基础医学   1806篇
口腔科学   356篇
临床医学   1532篇
内科学   2343篇
皮肤病学   304篇
神经病学   850篇
特种医学   2131篇
外国民族医学   9篇
外科学   977篇
综合类   2617篇
现状与发展   2篇
一般理论   1篇
预防医学   3070篇
眼科学   145篇
药学   4347篇
  21篇
中国医学   963篇
肿瘤学   1977篇
  2024年   178篇
  2023年   331篇
  2022年   659篇
  2021年   913篇
  2020年   880篇
  2019年   758篇
  2018年   829篇
  2017年   838篇
  2016年   872篇
  2015年   810篇
  2014年   1530篇
  2013年   1715篇
  2012年   1278篇
  2011年   1380篇
  2010年   1044篇
  2009年   964篇
  2008年   929篇
  2007年   847篇
  2006年   740篇
  2005年   624篇
  2004年   548篇
  2003年   529篇
  2002年   453篇
  2001年   395篇
  2000年   319篇
  1999年   318篇
  1998年   270篇
  1997年   266篇
  1996年   217篇
  1995年   217篇
  1994年   202篇
  1993年   187篇
  1992年   163篇
  1991年   164篇
  1990年   152篇
  1989年   169篇
  1988年   145篇
  1987年   122篇
  1986年   120篇
  1985年   160篇
  1984年   130篇
  1983年   86篇
  1982年   101篇
  1981年   79篇
  1980年   78篇
  1979年   81篇
  1978年   46篇
  1977年   61篇
  1976年   38篇
  1975年   29篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
BackgroundPlatelets play a vital role in the neoplastic process. Platelet parameters are hence an important source of information concerning ongoing neoplastic disease. The aim of the study is to assess the impact of selected platelet parameters on the survival of patients with non-small cell lung cancer (NSCLC).MethodsThe study included 532 (174 female and 358 male) patients aged 36–84 years (mean age 63.6 years) operated on due to NSCLC, staged IA–IIIA. Before the operation, all patients received a blood morphology test. The following parameters were subjected to statistical analysis: platelet count, mean platelet volume (MPV) parameter, platelet distribution width (PDW) parameter, platelet-to-lymphocyte ratio (PLR) and systemic immune-inflammation (SII) index. These findings were compared with the clinical data of the patients, and the probability of overall survival was analyzed.ResultsThe univariate analysis revealed a correspondence between PDW, MPV, PLR and SII index and patient survival. The multivariate analysis including patient clinical data found the following factors to have negative prognostic value for patients operated on due to NSCLC: male sex, advancement stage of neoplastic disease and Charlson Comorbidity Index (CCI) above 4, and PLR >144.ConclusionsPDW value, PLR and SII index are independent prognostic factors. In the multi-factor model, male sex, the advancement stage of the neoplastic disease, CCI above 4 and PLR lower than 144 had the greatest prognostic value.  相似文献   
92.
鼻咽癌常规放疗中面颈联合野的剂量分布研究   总被引:1,自引:0,他引:1  
目的分析鼻咽癌常规放疗中面颈联合野的剂量分布图以了解剂量分布上存在的问题。方法采用美国ADAC公司的Pinnacle治疗计划系统对1例鼻咽癌患者(福州分期为T2N0M0Ⅱ期)行双侧面颈联合野和中下颈前切野常规定位,再用CT模拟定位机进行CT扫描,把CT影像传送到Pinnacle治疗计划系统进行图像重建及照射野重建,再进行二维计划剂量运算,从而得到各层的剂量分布曲线。结果100%等剂量曲线仅能全包鼻咽腔和蝶窦底壁;105%等剂量曲线全包口咽和射野内的全部颈段脊髓,110%等剂量曲线包口咽的下部分和颈3、4段部分脊髓;95%和90%等剂量曲线穿过蝶窦和斜坡中央;50%的等剂量曲线与射野各界重叠。两野共线处附近组织位于110%等剂量曲线内,最高剂量达220%。结论面颈联合野剂量分布存在着以下几点缺陷:(1)蝶窦和斜坡均在100%~50%的等剂量曲线之间,故存在颅底和斜坡欠量;(2)口咽部剂量在105%~110%的等剂量曲线之间,为高量区,故放射性咽炎常见;(3)颈段脊髓均位于105%~110%高剂量区,易产生放射性脊髓病;(4)两野共线处出现剂量重叠。  相似文献   
93.
The railway wheel is the key component of high-speed railway train. To assure the safety in service, higher requirements are put forward in this study for the composition, microstructure uniformity, and comprehensive properties of wheel materials. In this paper, the high throughput quantitative distribution characterization methods of composition, microstructure, inclusions and Vickers hardness of high-speed railway wheel materials based on the spark source original position analysis technique, high throughput scanning electron microscope (SEM) combined with image batch processing technology, and automatic two-dimensional quantitative distribution analysis technique of inclusions and micro hardness have been studied. The distribution trend of the content of nine elements, size and quantity of sulfides and oxides, ferrite area fraction, and Vickers hardness from the wheel tread surface to the radial depth of about 50 mm below the surface has been discussed. The influence of inclusions distribution on the element segregation and the effect of rim-chilling process with different water spraying angle on the distribution of microstructure and micro hardness have been investigated. It was found that unsynchronized cooling on both sides of the rim altered the phase behavior of ferrite and pearlite and obvious inhomogeneity distribution of ferrite appeared, which led to the asymmetrical Vickers hardness in areas near or away from the flange. Based on the quantitative characterization of area fraction and micro hardness on the same location of wheel rim, a statistical mapping relationship between ferrite area fraction and Vickers hardness was established.  相似文献   
94.
目的 对饮用水硝酸盐进行健康风险评估,为水质干预决策提供技术依据。 方法 对2016~2020年淄博市2 575份城乡饮用水样品检测硝酸盐含量,采用我国《化学物质环境健康风险评估技术指南》(WS/T 777-2021)的环境健康风险评价模型,分析不同年度、不同监测点类型、不同水源、不同处理方式的硝酸盐含量和非致癌健康风险的时空分布特征。 结果 2016~2020年共检测水样2 575份,硝酸盐超标率为10.76%。饮用水硝酸盐含量具有空间聚集性,高值主要集中在沂源县中部和东部、博山区西南部,低值集中在高青县和桓台县。饮用水硝酸盐含量和非致癌健康风险总体呈现逐年升高趋势,农村水高于城区水、地下水高于地表水、未处理水高于处理水。5年总体平均非致癌风险为0.21,对人体产生的非致癌风险较低;最高非致癌风险为1.99,主要集中在沂源县,对人体存在长期暴露的非致癌健康风险。 结论 淄博市局部区域饮用水硝酸盐污染较严重,存在非致癌健康风险,应引起关注并采取水质干预措施。  相似文献   
95.
The ACR Dose Index Registry (DIR) provides a new source of clinical radiation exposure data that has not been used previously to establish or update the relative radiation level (RRL) values in the ACR Appropriateness Criteria (AC). The results of a recent review of DIR data for 10 common CT examinations were compared with current ACR AC RRL values for the same procedures. The AC RRL values were previously determined by consensus of members of the AC Radiation Exposure Subcommittee based on reference radiation dose values from the literature (when available) and anecdotal information from individual members’ clinical practices and experiences. For 7 of the 10 examination types reviewed, DIR data agreed with existing RRL values. For 3 of 10 examination types, DIR data reflected lower dose values than currently rated in the AC. The Radiation Exposure Subcommittee will revise these RRL assignments in a forthcoming update to the AC (in October 2018) and will continue to monitor the DIR and associated reviews and analyses to refine RRL assignments for additional examination types. Given recent attention and efforts to reduce radiation exposure in CT and other imaging modalities, it is likely that other examination types will require revision of RRL assignments once information from the DIR database is considered.  相似文献   
96.
Purpose  The aim of this study was to assess the variation of probe rotation angles for detecting a single needle using sagittal images of transrectal ultrasonography (TRUS). Materials and methods  A phantom study was performed. One needle was inserted through each of 10 holes of the template, and variations in the probe rotation angles for detecting the needle were measured. Results  The mean variation of probe rotation for detecting a single needle was 17.0° (range 4°–25°). Slightly broader variation was seen for the needle in holes farther away from the probe. Conclusion  Probe rotation angles for detecting a single needle displayed considerable variation. Seed locations recognized on sagittal imaging by TRUS are thus indeterminate, and real-time dose calculations using TRUS for 125I seed implantation should be used with care.  相似文献   
97.
Nanoliposomal irinotecan (nal-IRI) plus 5-fluorouracil and leucovorin (NalFL) comprises the current standard for gemcitabine-failed metastatic pancreatic ductal adenocarcinoma (PDAC). As liposomes generally accumulate in the spleen, we evaluated the impact of spleen volume on prognosis. We enrolled patients with metastatic PDAC who failed gemcitabine-based therapy and were initiated on NalFL between August 2018 and November 2020. The spleen volume before NalFL administration was evaluated. They were stratified into dose subgroups (i.e. low, < 48 mg/m2; intermediate, 48 - < 64 mg/m2; high, ≥ 64 mg/m2) by the average nal-IRI dose during the entire treatment, and multivariate analysis of overall survival (OS) was performed. We included 547 patients with a median age of 63 years (range, 27-89 years) and a median of 1 (range, 0-7) palliative chemotherapy regimen. The median spleen volume was 245 mL (range, 82-817 mL). Among patients with splenomegaly (≥ 245 mL), the low-dose subgroup had the worst median time to treatment failure (TTF, 1.8 months vs. 2.5 months vs. 2.5 months, P = 0.020) and OS (3.3 months vs. 5.9 months vs. 6.6 months, P = 0.018) as against no prognostic impact in patients without splenomegaly. In the multivariate analysis of patients with splenomegaly, performance status (PS) ≥ 2, body surface area (BSA) < 1.6 m2, prior fluoropyrimidine use, liver metastasis, and low-dose subgroup were independent poor prognostic factors. A low average nal-IRI dose was significantly associated with poor prognosis, especially among patients with splenomegaly. Further pharmacological studies should validate the relevance of spleen volume on the treatment outcomes of nal-IRI.  相似文献   
98.
目的大体重患者在冠脉CTA前瞻性序列扫描中运用ECG管电流调制技术评价X线吸收剂量及临床应用。方法40例体重指数(BMI)24的患者在冠脉CTA检查中随机分为两组:A组20例采用ECG管电流调制技术(ATCM),心率70次/分时,扫描范围为20%-80%R-R间期,设60%-80%R-R间期组为全剂量扫描范围;心率70次/分时,扫描范围为20%-80%R-R间期,设35%-55%R-R间期组为全剂量扫描。B组20例均选用20%-80%R-R间期组为全剂量扫描;比较两组病例的图像质量及辐射剂量。结果 A组平均辐射剂量(6.91±2.78),B组为(10.43±3.36),A组比B组减少了33.77%的辐射剂量;辐射剂量有统计学差异(P0.05),而图像质量无明显差别。结论在前瞻性序列扫描中运用ECG管电流调制技术可以明显降低大体重患者的辐射剂量。  相似文献   
99.
在目前我国高校财力资金不足的情况下,如何更好的加以配置,直接关系到高校的办学效益和办学质量。财力资金的合理配置,已成为高校的头等大事。  相似文献   
100.
目的:研究不同烧结次数对氧化钇稳定四方相氧化锆(Y-TZP)陶瓷机械性能的影响。方法:制作Y-TZP瓷片,分为3组,分别烧结1、3、5次,每组再分为3个亚组,分别为在压力灭菌锅内进行水热老化处理10、20 h模拟Y-TZP的低温老化组,烧结后未进行老化的作为对照组。如此,实验共分为9组(1-10、1-20、1-C、3-10、3-20、3-C、5-10、5-20、5-C),测量每组试件的3点弯曲强度,压痕法测算其断裂韧性,并利用WEIBULL分布分析弯曲强度测量结果的可靠性。结果:9组试件的弯曲强度及断裂韧性无统计学差异(P>0.05),WEIBULL分析同样证实这一结果。结论:烧结次数的增加不会加速Y-TZP的低温老化效应,Y-TZP修复体制作过程中可能需要的多次烧结对Y-TZP材料本身的机械性能无明显影响。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号